1. Field of the Invention
The present invention relates to a packaging substrate for electronic parts or elements such as semiconductor chips and to an electronic device having the packaged electronic elements. More particularly, the present invention relates to a packaging substrate designed to receive thereon electronic elements using different packaging methods, and an electronic device having the electronic elements packaged using such a packaging substrate.
2. Description of the Related Art
At present, a wide variety of packaging substrates are commercially available as substrates for packaging electronic parts such as semiconductor chips. Some packaging substrates are designed to receive on the same substrate different types of electronic parts such as semiconductor chips for a microprocessor and semiconductor chips for a memory. On these packaging substrates, the semiconductor chips are sometimes mounted with different packaging methods, that is, one type of semiconductor chip is mounted with a wire bonding method, and another type of semiconductor chip is mounted with a flip chip bonding method.
Generally, when a wire bonding method is used in the packaging of semiconductor chips on the packaging substrate, a bonding pad is formed on predetermined sites of a surface of the substrate. The bonding pad is generally produced by forming a wiring pattern from a wiring material such as copper (Cu), followed by forming on the wiring pattern a plating layer consisting of nickel (Ni) plating and gold (Au) plating. The plating layer is applied to improve the bonding strength between the bonding pad and the bonding wire.
On the other hand, when a flip chip bonding method is used in the packaging of semiconductor chips, a solder bump is generally applied to between a bonding pad of the packaging substrate and an external terminal or electrode of the semiconductor chips. Further, when the electrode of the semiconductor chips has a protruded electrode, comprising gold (Au) as a principal component thereof, on a tip position thereof, a solder material such as Snxe2x80x94Pb or Snxe2x80x94Ag is previously applied to the bonding pad of the substrate, and then the protruded Au electrode is bonded through the solder material to the bonding pad.
Thus, when the semiconductor chip designed for wire bonding and the semiconductor chip designed for flip chip bonding have to be mounted on the same packaging substrate, to avoid any problems caused due to packaging of two different semiconductor chips, bonding pads for the wire bonding and flip chip bonding were typically produced by forming wiring patterns from a suitable wiring material such as copper on the substrate. The wiring patterns were then plated with nickel and gold to form bonding pads which are suitable for wire bonding. Some of the thus obtained bonding pads were further coated with a soldering material to form solder-coated bonding pads suitable for flip chip bonding.
The above-described prior art method for forming the different bonding pads in the packaging substrate and the semiconductor device using the produced packaging substrate with the different bonding pads will be further described hereinafter with reference to FIG. 1 showing the constitution of the prior art packaging substrate 11 having the area A designed to receive thereon an electronic element through wire bonding and the area B designed to receive thereon an electronic element through flip chip bonding, FIG. 2 showing the construction of the electronic device, particularly semiconductor device 10, using the packaging substrate of FIG. 1, and FIGS. 3A and 3B showing the constitution of the different bonding pads 12 and 55 used in the semiconductor device 10 of FIG. 2.
As illustrated in FIG. 2, the semiconductor device 10 comprises a packaging substrate 11 and one main surface of the substrate 11 bears both of a semiconductor chip 20 for wire bonding and a semiconductor chip 30 for flip chip bonding, while another main surface of the substrate 11 opposed to the chips-bearing surface has a group of solder bumps 40 acting as an external connection terminal. The chip-bearing surface of the substrate 11 has formed thereon a wiring pattern 17 made of copper, and an insulating material 18 is further deposited except for the areas of the bonding pads 12 and 55.
Referring to the area A of the packaging substrate 11, there is illustrated the semiconductor chip 20 mounted on and bonded through an adhesion layer 21 to the substrate 11, and its I/O terminal (not shown) is electrically connected through an Au bonding wire 22 to a bonding pad 12. As shown in FIG. 3A, the bonding pad 12 is formed on the Cu wiring pattern 17 of the substrate 11, and is constituted from a plating layer 14 formed by sequentially plating on a surface of the wiring pattern 17 a nickel plating 14a and a gold plating 14b. 
Referring to the area B of the packaging substrate 11, there is illustrated the semiconductor chip 30 mounted through flip chip bonding to the substrate 11. After positioning of the protruded electrode 32 of the semiconductor chip 30 to the bonding pad 55 formed on the wiring pattern 17 of the substrate 11, the semiconductor chip 30 is bonded to the bonding pad 55 through a solder material 56 applied to a surface of the pad 55. The protruded electrode 32 is generally formed in the form of an Au stud bump. As shown in FIG. 3B, the bonding pad 55 has a constitution similar to that of the bonding pad 12 except that its plating layer 14 consisting of a Ni plating 14a and an Au plating 14b further has a solder layer 56 to which the protruded electrode 32 is embedded for the bonding purpose. The space between the substrate 11 and the semiconductor chip 30 is filled with an electrically insulating under-filling resin 34. Further, in the semiconductor device 10, semiconductor chips 20 and 30 as well as other parts including the bonding wire 22 are covered and protected with an electrically insulating sealing resin 36.
However, the prior art semiconductor devices such as those described above, referring to the attached drawings, suffer from important problems. The first problem is a problem caused in the bonding pad 55 for flip chip bonding due to diffusion of the gold from the Au plating 14b appearing on a surface of the bonding pad 55 to the solder layer 56. Since an amount of the solder on the bonding pad 55 is low, a melting point of the solder layer 56 can be remarkably increased as a result of inclusion of the gold in the solder.
The problem of an increase in the melting point of the solder is particularly serious when the electrodes 32 are densely disposed on the semiconductor chip 30, because a bonding surface of the bonding pads 55 is reduced with an increase of the distribution density of the electrodes 32, and thus an amount of the solder to be applied to each bonding pad 55 is reduced. In other words, a ratio of the gold diffused in the solder is further increased, and as a result, the melting point of the solder is further increased.
In addition to the increase in the melting point of the solder, the melting point of the solder can be varied as a result of variation of the amount of the solder supplied to each bonding pad 55. The variation of the amount of the solder is caused, because a pitch between the adjacent bonding pads 55 is narrowed in conformity with an increase in the distribution density of the electrodes 32. As the melting point of the solder can be varied within about 50xc2x0 C., it becomes difficult to ensure a reliable solder bonding between the semiconductor chip 30 and the substrate 11.
Another problem arises due to the application of a solder to the bonding pad and other parts of the wiring pattern. For example, when a solder should be coated to the bonding pad, it is conventionally carried out to supply and print a solder paste at a predetermined pattern on the pad. However, when a pitch between the adjacent bonding pads is as small as 100 xcexcm or less as in the packaging substrate for flip chip bonding of the semiconductor chips, there arises a problem due to the constitution of the bonding pads, that is, a short-circuiting problem can be caused as a result of bridging of the solder between the pads.
Further, to ease an application of the solder to the bonding pads, it is possible to simultaneously coat a solder to the bonding pads for wire bonding, in addition to coating of the solder to the bonding pads for flip chip bonding. However, in such a case, as a surface of the bonding pads for wire bonding is also covered with the coated solder, it becomes difficult to wire bond of the pads, thereby extending the time for the wire bonding.
The present invention is directed to solve the above-described problems in the prior art packaging substrates and the semiconductor and other devices using the packaging substrate.
It is an object of the present invention to provide a packaging substrate capable of packaging electronic devices such as semiconductor chips using different packaging methods, i.e., wire bonding packaging and flip chip packaging, without causing any problems such as defective solder bonding, short-circuiting of the wiring pattern, and troublesome and time-consuming wire bonding, but with high reliability.
It is another object of the present invention to provide an electronic device having mounted on a substrate thereof, with high reliability, one or more electronic elements mounted by wire bonding and one or more electronic elements mounted by flip-chip bonding.
These and other objects of the present invention will be easily understood from the following detailed description of the preferred embodiments of the present invention.
The inventor of the present invention has conducted intensive studies for accomplishing the objects described above and, surprisingly, the inventor has discovered that the above objects can be accomplished if the bonding pad for flip chip bonding of semiconductor chips and other electronic elements is constituted to be free of gold (Au) and nickel (Ni) plating.
According to one aspect of the present invention, there is provided a packaging substrate for electronic elements, on which substrate two or more electronic elements are mounted through flip chip bonding and wire bonding, in which
the packaging substrate comprises at least one first area designed to receive thereon an electronic element through flip chip bonding and at least one second area designed to receive thereon an electronic element through wire bonding,
the first area of the packaging substrate has at least one bonding pad to which an external terminal of the electronic element is connected, and the bonding pad comprises a copper-based material having applied on a surface thereof a coating of a solder material, and
the second area of the packaging substrate has at least one bonding pad to which an end portion of the bonding wire extended from an external terminal of the electronic element is connected, and the bonding pad comprises a copper-based material having applied on a surface thereof a plating layer comprising a combination of nickel plating and gold plating.
According to another aspect of the present invention, there is provided an electronic device comprising a packaging substrate and two or more electronic elements mounted through flip chip bonding and wire bonding on the packaging substrate, in which
the packaging substrate comprises at least one first area designed to receive thereon an electronic element through flip chip bonding and at least one second area designed to receive thereon an electronic element through wire bonding,
the first area of the packaging substrate has a bonding pad comprising a copper-based material having applied on a surface thereof a coating of a solder material, and an electronic element for flip chip bonding is mounted on the first area of the packaging substrate, while the bonding pad is electrically connected with an external terminal of the electronic element, and
the second area of the packaging substrate has a bonding pad comprising a copper-based material having applied on a surface thereof a plating layer comprising a combination of nickel plating and gold plating, and an electronic element for wire bonding is mounted on the second area of the packaging substrate, while the bonding pad is electrically connected through a bonding wire with an external terminal of the electronic element.